Fuel cells are electrochemical cells in which a free energy change resulting from a fuel oxidation reaction is converted into electrical energy. End uses for fuel cells include battery replacement, mini- and microelectronics, automotive engines and other transportation power generators, power plants, and many others. One advantage of fuel cells is that they are substantially pollution-free.
In hydrogen/oxygen fuel cells, hydrogen gas is oxidized to form water, with a useful electrical current produced as a byproduct of the oxidation reaction. A solid polymer membrane electrolyte layer can be employed to separate the hydrogen fuel from the oxygen. The anode and cathode are arranged on opposite faces of the membrane. Electron flow along the electrical connection between the anode and the cathode provides electrical power to load(s) interposed in circuit with the electrical connection between the anode and the cathode. Hydrogen fuel cells are impractical for many applications, however, because of difficulties related to storing and handling hydrogen gas.
Organic fuel cells may prove useful in many applications as an alternative to hydrogen fuel cells. In an organic fuel cell, an organic fuel such as methanol is oxidized to carbon dioxide at an anode, while air or oxygen is simultaneously reduced to water at a cathode. One advantage over hydrogen fuel cells is that organic/air fuel cells can be operated with a liquid organic fuel. This diminishes or eliminates problems associated with hydrogen gas handling and storage. Some organic fuel cells require initial conversion of the organic fuel to hydrogen gas by a reformer. These are referred to as indirect fuel cells.
The presence of a reformer increases cell size, cost, complexity and start up time. Other types of organic fuel cells, called direct fuel cells, avoid these disadvantages by directly oxidizing the organic fuel without conversion to hydrogen gas. Until recently, methanol and other alcohols were the fuel of choice in the development of direct fuel cells, and most research focused on the use of these fuels.
An advance in the art is presented in U.S. Patent Application Publication No. 2003/0198852 (“the '852 publication”) and 2004/0115518 (“the '518 publication”). Embodiments described in these applications disclose formic acid fuel cells with high power densities and current output. Exemplary power densities of 15 mW/cm2 and much higher were achieved at low operating temperatures. Additionally, embodiments described in those applications provided for compact fuel cells.
While fuel cells will have different configurations for different applications, the compact fuel cells will be suitable for replacement in small portable electronics, e.g., cellular handsets and personal digital assistants (PDAs). As an example, cellular handsets typically require a certain amount of power (usually 3 watts) which should fit within a cavity of approximately 10 cc to 30 cc. In order for a fuel cell technology to accomplish this, it must have the capability of operating at a high power density. Direct formic acid fuel cells in accordance with embodiments of the '852 publication and the '518 publication have been demonstrated as suitable to deliver such power in the small form factor suited to small portable electronics.
Commercial bulk grades of formic acid are made by a number of processes. Processes for making formic acid are disclosed in U.S. Pat. Nos. 5,879,915, 5,869,739, 5,763,662, 5,633,402, 5,599,979, 5,393,922, 4,262,140, 4,126,748 and 2,407,157. Commercial bulk grades of formic acid are used in a variety of industries and processes. It is used, for example in animal feed additives, to dye clothing, and in the manufacture of vinyl resin plastics. It is also used to manufacture aspartame. There are also commercial purified grades of formic acid. The commercial purified grades have a smaller market. The commercial purified grades are used, for example, as a solvent in high performance liquid chromatography (HPLC) and as solvents for other measurement techniques.